Proceedings of the Annual Stability Conference Structural Stability Research Council St. Louis, Missouri, April 16-20, 2013 Shell buckling evaluation of thin-walled steel tanks filled at low liquid level according to current design codes C. Maraveas 1 , K. Miamis 2 Abstract The structural stability of thin-walled steel tanks becomes a major safety issue when these operate at low levels of contained liquid. Despite numerous tank failures due to buckling of their circumferential shell, provisions in current codes do not provide cost-efficient or high-safety level solutions regarding this phenomenon. For example, the American standard API 650, which has worldwide applications, proposes only an empirical design method for stiffening the tank shell based on its thickness, height and the design wind velocity. More recent codes, such as the European standard EN1993-1-6, provide analytical relationships for evaluating the buckling resistance of shells, with stability being verified by relevant checks against appropriate design stresses. However, their provisions have not yet seen many field applications and results raise, in certain cases, doubts regarding the efficiency of the design. This paper presents a direct comparison between these two standards by attempting to evaluate the buckling resistance of two existing thin-walled steel tanks, filled at a low liquid level. Both tanks have large diameters (47m and 88m approximately), variable wall thickness, are self-supported (unanchored) and one of them supports a conical roof. The design stresses required by EN1993-1-6 were obtained from finite element simulations of the tanks (linear elastic analyses were performed) which included application of the actions specified in the provisions of the Eurocode. Results from both standards are discussed in detail, comparisons are made and discrepancies between the two standards are highlighted. Comments and conclusions to be drawn will help improve current specifications and resolve issues related to the safe design of liquid storage tanks filled at low liquid levels. 1. Introduction The safe and cost-efficient design of large diameter cylindrical steel tanks used for oil storage has always been a challenge for the civil engineering community. Their structural failure poses a severe threat to public safety (i.e explosions), might lead to environmental degradation of the surrounding area and can induce onerous financial consequences. Such tanks are typically designed to operate at a high level of contained liquid, mainly due to overall stability reasons (i.e. resistance against sliding and overturning). As a result, current codes focus on the limitation 1 C.MARAVEAS PARTNERSHIP - Consulting Engineers, Athens, Greece, < [email protected]> 2 C.MARAVEAS PARTNERSHIP - Consulting Engineers, Athens, Greece, < [email protected]> 710
Shell buckling evaluation of thin-walled steel tanks filled at low liquid level according to current design codes
May 16, 2023
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